Gas oil hydrocracking process to produce a high octane gasoline



March 5, 1963 T; S. MERTES GAS OIL HYDROCRACKING PROCESS TO PRODUCE AHIGH OCTANE GASOLINE Filed Sept. 15, 1960 Catalytic Straight Run Gas OilGas Oil H2 l0 ll Makeup I2 30 \A i Fr ction /35 Extraction mma aNaphthene Makeup l3 '6 Saturate g Fraction 3l\ Temperature //32 H2Cracking t/l'l Si lice ous Catalyst with l4 Hydrogenating Temperaturecomponent Cracking 2o 24 (AlBr -HBr) 36 H Recycle HBr 37 DistillationDistillation Residuum R O -L|ghter Hydrocarbons Hydrocarbons AboveGasoline u \m Fraction -Isobutane G Naphthene 39 W 0 -6 Paraffins HeavyGasoline Fraction High Antiknock Gasoline INVENTOR. THOMAS S. MERTESATTORNEY United States Patent Qfifice 3,080,311 Phtented Mar. 5, 1963Jersey Filed Sept. 15, 1960,.Ser. No. 56,198 2 Claims. (Cl. 208-78) Thisinvention relates to a combination process for producing high antiknockgasoline from both straight run and catalytic gas oils by hydrocracking.

In application Serial No. 25,509, filed April 29*, 1960, now abandoned,a process is described which is capable of converting high boilingsaturate hydrocarbons, such as the staurate portion of gas oils,substantially completely into saturate hydrocarbons boiling in thegasoline range. These product hydrocarbons, which are mainly C -Cisopar-afiins and C and higher naphthenes, have high antiknock valuesand are suitable as components of high antiknock gasolines. Theprocess'involves hydrocracking at relatively low temperature utilizingAlBr -HBr =as catalyst, and the reaction must be carried out in thepresence of a substantial amount of one or more naphthenes of the C -Crange. The reaction system is homogeneous and the reaction proceedscleanly without any sludge forma tion.

One drawback to the process described in said application is that thecharge stock must be essentially free of aromatics, since thesehydrocarbons form sludges with the catalyst and prevent it fromfunctioning in the manner desired. This circumstance necessitates theuse of a feed preparation step for removal of essentially all of the momatics from the gas oil feed stock. Since the resultin aromatic productgenerally would have to be sold as residual fuel oil at relatively lowvalue compared to gasoline, this procedure, in effect, results in adowngrading of a portion of the gas oil stock.

The present invention involves a manner of utilizing the foregoingprocess advantageously in a combination system for converting bothstraight run gas oil and catalytic gas oil into high antiknock gasoline.Catalytic gas oils, which typically may have aromatic contents in therange of 3060% by volume, are not suitable charge stocks for theabove-discussed process in view of the cost of separating the relativelyhigh proportion of aromatics from the saturates and the low value of thearomatic portion. They are also not suitable charge stocks forconventional catalytic cracking processes because of the refractorycharacter of the aromatics. However they can be cracked effectively intohigh octane gasoline by hydrocracking under conditions involving the useof a large proportion of hydrogen and a siliceous cracking catalystcontaining a hydrogenating component.

A process of this type is described in Scott United States Patent No.2,944,006. It involves the use of a catalyst containing a hydrogenatingcomponent, which is either nickel sulfide or cobalt sulfide, supportedon an active siliceous cracking catalyst such as silica-alumina,silicarnagnesia, silica-zirconia and acid activated clays. The processis operated at temperatures between 350 and 700 F., with at least 1500s.c.f. of H per barrel of con- Version product boiling below the chargeand hydrogen partial pressure generally in the range of 500-2000 p.s.ig.The antiknock value of the gasoline product increases as the aromaticcontent of the charge increases. Normally the operation effects aconversion of 50-70% per pass and the material which boils higher thanthe desired gasoline product is totally recycled- Another process forhydrocracking catalytic gas oils is described in Hansford United StatesPatent No. 2,885 ,349. This process utilizes an acidic oxide crackingcatalyst, such as silica-alumina, containing a hydrogenating componentwhich is chromium sulfide derived by reduction of chromium sulfate.Conditions of operation include temperatures in the range of 7 50-1050F., hydrogen input of 1000-10000 s.c.f. per barrel of feed and hydrogenpressures in the range of 500-5000 p.s.i.g.

In the present invention processes of the types mentioned in theabove-discussed patent application and patents are utilized in acombination operation wherein both straight run gas oil and catalyticgas oil are converted to gasoline in the most eflicacious manner.According to the invention the straight run gas oil stock is treated ina manner to separate essentially all of the aromatics from the saturatefraction. The aromatics are then blended with the catalytic gas oilstock and the mixture is subjected to catalytic hydrocra-ckingconditions in the presence of hydrogen and a siliceous cracking catalystcontaining a hydrogenating component to produce catalytic gasoline. Thesaturate fraction is blended with a naphthene or mixture of naphtheneshaving 7-9 carbon atoms to form a blend containing 25-90% by Weight ofthe naphthene, and AlBr is dissolved in the mixturein amount of 25- byweight based on the total hydrocarbons. The mixture is then contacted inthe presence of HBr with hydrogen under a partial pressure of 25-500p.s.i. and at a temperature in the range of 0-100 C. for a timesufiicient to convert at least a major portion of the charge saturatecontent to hydrocarbons boiling in the gasoline range. In this reactionthe C -C naphthene remains largely unconverted and can be separated fromthe reaction product and recycled. Also the hydrocarbons boiling abovethe gasoline range can be totally recycled, so that no material boilingabove gasoline results from the operation.

The invention is described more specifically in conjunction with theaccompanying drawing which is a schematic illustration of the presentprocess. Referring to the drawing, straight run and catalytic gas oilsenter the system, respectively, through lines 10 and 11. The straightrun gas oil first goes to an extraction zone 12 wherein the aromaticsare substantially completely separated from the saturates. While theextraction step could be carried out by solvent extraction utilizing anaromatic-selective solvent, e.g. furfural, and sufficiently efiicientextraction conditions to attain the necessary degree of separation, thiswould be costly in view of'the fact that the saturate product needs tobe essentially aromatic-free. A distinctly better way of eiiecting theseparation is by selective adsorption by means of silica gel. Aparticularly suitable selective adsorption process for this step is theArosorb Process which is operated in cyclic manner as described on pages109-113 of Petroleum Refiner, vol. 31, No. 5

(May 1952 issue). In such process, the charge stock, preferably dilutedwith a low boiling saturate solvent such as pentane, is passed through abed of silica gel until the capacity of the bed for adsorbing chargearomatics is largely but not entirely depleted, after which a sufficientquantity of desorbent to desorb the charge aromatics completely ispassed through the bed. The desorbent, which preferably comprises acomponent of high adsorbability such as benzene together with acomponent of low adsorbability such as pentane, is so selected that itsboiling range is sutiiciently below the boiling range of the chargestock to enable easy separation of charge and desorbent components bydistillation.

The efiluent from the adsorbent case, during each cycle of operation, iscollected in two or more portions, one of which comprises chargesaturates and desorbent, and another ofwhich comprises charge aromaticsand desorbent. These portions are then separately subjected tofractional distillation in order to recover a charge saturate fraction,a charge aromatics fraction, and desorbent for recycle .to the process.For the present purpose the selective adsorption step is mosteconomically operated under conditions such that the saturate fractionobtained is essentially aromatic-free while the aromatic fractioncontains a substantial proportion of saturates, e.g. 20% by volume.-This allows the separation to be effected more readi ly than would bethe case if a pure aroma-tic fraction also were to be produced. Thesaturates in the aromatic fraction are not reduced in value since theyare readily cracked to gasoline in the subsequent hydrocracking of thearomatic fraction.

The aromatic-free saturate fraction obtained from extraction zone 12 issent through line 13 to a low temperature cracking zone 14. Prior toentering this zone the saturate fraction is admixed with a recyclestream from line 15 which stream contains one or more naphthenes of theC -C range (indicated in the drawing as O; naphthene). A small amount ofmake-up C naphthene can be added to the system through line 16. Theproportion of the hydrocarbon streams should be such that the C -Cnaphthene content of the mixture is in the range of 25-90% by weight,more preferably, 30-50%. Any naphthene of the C -C range can be used forthis purpose. While it remains mainly unconverted in the sys tem, itspresence in reaction zone 14 is important for obraining a clean reactionand avoiding sludge formation.

The catalyst used in reaction Zone 14 is AlBr in combination with HBr.The amount of AlBr present should be 25-l00% based on the weight oftotal hydrocarbons in zone 14. The amount of HBr used is notparticularly important as long as at least a small amount is present,for example, 025% by weight based on the hydrocarbons. Hydrogen is fedinto reaction zone 14 through line 17 and the amount so introducedshould be sufiicient to maintain a hydrogen partial pressure in therange of 25-500 psi. The reaction temperature should be maintained inthe range of -100 C., more preferably 25-75 C., and the reaction mixtureshould be agitated continuously to effect intimate contact with thehydrogen. The reaction mixture is homogeneous, and under the conditionsspecified essentially no sludge formation occurs. A sufiicient residencetime in the reactor should be allowed to convert at least a majorportion of the gas oil saturates to hydrocarbons boiling in the gasolinerange.

The reaction mixture from zone 14 passes through line 18 to adistillation zone indicated diagrammatically at 19. I-lBr is firststripped from the mixture and passes back to cracking zone 14 throughline 20. Isobutane, which is invariably produced in substantial yield,is removed next as indicated by line 21 and can be utilized in anotherprocess such as alkylation. The C -C parafiin products, which arepreponderantly isoparaflins of high antiknock value, are removed asindicated by line 22. Then the C naphthene (or if desired a mixture of C-C naphthenes) can be recovered as indicated by line 23 and a part orall of this material is recycled through lines 24 and to cracking Zone14 to maintain the necessary naphthene content of the reaction mixture.Only a small amount of the naphthene originally used is converted toother products in the reaction and hence in no event is any largemake-up of naphthene through line 16 required. In fact, when only a Cnaphthene such as methylcyclohexane is originally used, not only is theextent of disappearance of the C naphthene small but C and C naphthenesgenerally are produced in substantial amounts from the gas oilsaturates. Hence sufiicient C -C naphthene can be recycled to maintainthe desired naphthene content in zone 14 and no make-up whatever isrequired through line 16.

A heavy gasoline fraction, which boils above the cut point of thenaphthene cut, is distilled and removed through line 25, leaving asresidue hydrocarbons boiling above the gasoline range with AlBrdissolved therein or both dissolved and dispersed therein depending onAlBr concentration and the temperature. of the stream. This material isrecycled through lines 24 and 15 for re-use of the AlBr and furtherconversion of the hydrocarbons to gasoline. The heavy gasoline fractionis composed essentially entirely of naphthenes boiling above the cutpoint of the recycle naphthene fraction together with isoparaffins, andit also has a high antiknock value.

Referring back to the aromatic fraction which is obtained fromextraction zone 12 via line 30, this material is blended with thecatalytic gas oil from line it and with recycle material from line 31and the material is fed to cracking zone 32 which operates atconsiderably higher temperature than is used in cracking zone 14. Theproper temperature level in zone 32 depends to considerable extent uponthe particular catalyst being used but in any event falls within thegeneral range of 350-1050 F. The catalyst is composed of a hydrogenatingcomponent deposited on an active siliceous cracking catalyst support,such as described in the aforementioned United States Patent No.2,944,006 and Patent No. 2,885,349 wherein the hydrogenating componentsare nickel sulfide, cobalt sulfide or chromium sulfide. Otherhydrogenating components that can be used are the sulfides of iron,molybdenum and tungsten, the oxides of iron, nickel, chromium,molybdenum and tungsten, platinum, rubidium and rhodiurn. Hydrogen inamount of 1000-2500 s.c.f. per barrel of mixed hydrocarbon feed isintroduced through line 33 into cracking zone 32 and a hydrogen partialpressure in the range of 500-5000 p.s.i. is maintained therein. Thehydrogen stream is composed of recycle hydrogen from line 34 togetherwith make-up hydrogen admitted from line 35.

The efiluent which leaves cracking zone 32. via line 36 is passedthrough suitable separating means (not shown) for recovering the excesshydrogen and then into distillation zone 37. The hydrocarbons arefractionated to remove C, and lighter hydrocarbons as indicated by line33 and a debutanized gasoline as shown by line 39. The residuum,composed of hydrocarbons boiling above the gasoline range, can all bewithdrawn through line 40 as a fuel oil product but preferably is atleast mainly recycled through line 3-1 for further conversion togasoline. The gasoline fraction from line 39 can be blended with the C-C paratfins from line 22 and the heavy gasoline fraction from lines 25and 41 to yield a high quality gasoline product.

In order to illustrate advantages of the present process, the followingcomparison is made between a process operated according to the aforesaidapplication Serial No. 25,509 for the purpose of processing 10,000bbls./ day of straight run gas oil and the present process operated tohydrocrack a total of 10,000 bbls./ day of gas oils comprising 6,667hbls/day of straight run gas oil and 3,333 bbls/day of catalytic gasoil. It is assumed that the straight run and catalytic gas oils havearomatic contents of 20% and 40% by volume, respectively.

The following data show the processing capacities required for the twooperations and the products obtained:

From the data presented it can be seen that the present process requiresless total plant capacity and produces a considerably larger volume ofgasoline without any production of fuel oil. Also the gasoline producedhas an appreciably higher antiknock value.

I claim:

1. A process for cracking straight run gas oil and catalytic gas oilwhich comprises contacting a straight run gas oil stock With silica gelto obtain an aromatic fraction and a saturate fraction essentially freeof aromatics, blending said aromatic fraction with a catalytic gas oilstock, subjecting the blend of aromatic fraction and catalytic gas oilstock to catalytic hydrocracking conditions in the presence of hydrogenand a siliceous cracking catalyst containing a hydrogenating componentat 35 0-105 0 F. to form catalytic gasoline, forming a reaction mixturecomprising said saturate fraction and 25-90% by weight, based on thetotal hydrocarbon content of the reaction mixture, of monocyclicnaphthene having 7-9 carbon atoms yer molecule, said reaction mixturealso containing 25-100% by weight, based on the hydrocarbon content, ofAlBr contacting the reaction mixture in the presence of HBr withhydrogen under a partial pressure of hydrogen at 25-500 p.s.i. at atemperature in the range of 0100 C. for a time sufiicient to convert atleast a major portion of said saturate fraction in the reaction mixtureto hydrocarbons boiling in the gasoline range, and blending saidcatalytic gasoline and said hydrocarbons boiling in the gasoline rangeto yield a gasoline product of high anti-knock value.

2. A process according to claim 1 wherein said hydrogenating componentis selected from the group consisting of nickel sulfide, cobalt sulfide,and chromium sulfide.

References Cited in the file of this patent UNITED STATES PATENTS2,326,627 Eglofi et al Aug. 10, 1943 2,627,495 Lanning Feb. 3, 19532,885,349 Hansford May 5, 1959 2,908,628 Schneider et -al i Oct. 13,1959

1. A PROCESS FOR CRACKING STRAIGHT RUN GAS OIL AND CATALYTIC GAS OILWHICH COMPRISES CONTACTING A STRAIGHT RUN GAS OIL STOCK WITH SILICA GELTO OBTAIN AN AROMATIC FRACTION AND A SATURATE FRACTION ESSENTIALLY FREEOF AROMATICS, BLENDING SAID AROMATIC FRACTION WITH A CATALYTIC GAS OILSTOCK, SUBJECTING THE BLEND OF AROMATIC FRACTION AND CATALYTIC GAS OILSTOCK TO CATALYTIC HYDROCRACKING CONDITIONS IN THE PRESENCE OF HYDROGENAND A SILICEOUS CRACKING CATALYST CONTAINING A HYDROGENATING COMPONENTAT 350-1050*F. TO FORM CATALYTIC GASOLINE, FORMING A REACTION MIXTURECOMPRISING SAID SATURATE FRACTION AND 25-90% BY WEIGHT, BASED ON THETOTAL HYDROCARBON CONTENT OF THE REACTION MIXTURE, OF MONOCYCLICNAPHTHENE HAVING 7-9 CARBON ATOMS PER MOLECULE, SAID REACTION MIXTUREALSO CONTAINING 25-100% BY WEIGHT, BASED ON THE HYDROCARBON CONTENT, OFALBR3, CONTACTING THE REACTION MIXTURE IN THE